The invention concerns a hydrostatically balanced sliding bearing as well as hydraulic machines of different design, and general bearing applications with such a sliding bearing. Such sliding bearings are commonly known in various machines, particularly in hydrostatic pumps and motors. Movable and pressure bearing parts are often located in sliding bearings that are hydrostatically balanced through the supply of pressure fluid to the lubricant storing pocket. In axial piston machines with a swash plate design, this affects the slippers, which transfer the entire piston force at a relative movement of the slippers and the swash plate to the swash plate, the rotating cylinder block, the ball joint that connects piston and slipper, which transfers the entire piston force onto slipper. In variable hydrostatic machines the swash plate, that is under load due to the resulting pressure forces of all pistons, can be located in a hydrostatically balanced bearing. Axial piston units with bent axis design additionally have this possibility through axial location of the shaft with a driving flange that is under load due to the pressure forces transferred by the pistons. Similar sliding bearings can also be found in other hydrostatic machines, for example, in radial piston machines, gear pumps and motors, screw machines.
The disadvantages and problems of using hydrostatic bearings are numerous.
Hydrostatically balanced sliding bearings for optimum function need the pressurized fluids, which in hydrostatic machines, is usually taken from the high pressure line or the high pressure chambers of the machine. The pressure fluid that flows through these bearings to the low pressure side can no longer be used for energy transformation. Therefore, this flow has to be considered as a volumetric loss.
To reduce the loss and increase bearing hydrostatic stiffness, orifices are built into the intake channels to the areas under pressure. The orifice cross section in regular machines must be extremely small in order to achieve an appreciable bearing hydrostatic stiffness and in order to keep the volumetric loss within reasonable limits. The necessary small cross sections are very expensive. In some cases they cannot even be built. A capillary intended to serve as an orifice would have to be very long, in most cases greater than the length that is available in the machine. In addition, hydrostatic machines have certain places where orifices cannot be located, for example, the location of the cylinder block on the valve plate.
In order to keep the volumetric losses within reasonable limits, the pocket containing the lubricant currently has to be laid out so that the entire load is not hydrostatically compensated. Due to the excess remaining forces, the relatively moving parts are pressed together, ensuring a sufficient seal. The remaining force at standstill and at low relative speeds is transferred through the direct contact of the solid parts. The result is a boundary lubrication condition between the relatively moving parts due to the non-compensated excess force, which causes major frictional forces and wear. At higher speeds the excess force is usually almost completely compensated by the additional pressure field in the gap as a result of the hydrodynamic effect. The bearing operates as a hydrostatically balanced, hydrodynamic sliding bearing.
The circumstances described above are also described in detail by the example of a hydrostatic bearing that serves to transfer the piston forces to the swash plate in axial piston units with swash plate design. It is commonly known as a slipper and is well known as such in the art. The slipper principally represents a single surface axial bearing.